Partial Mash Bitter Diacetyl Rest Query

[jab]

Hey everyone, put this one on today.

2kg Ale Malt
1kg Light Dry Malt
230g Light Crystal Malt
120g Caramalt
20g Amarillo @ 8.6% (60min)
15g EK Goldings @ 4.7% (30min)
15g EK Goldings @ 4.7% (1min)
1 x Whirlfloc Tablet (15min)
1 Package Wyeast 1968 London ESB
Mash at 67 Degrees for 1 hour. Ended up making it a 23L batch to get the SG I wanted. Fermenting in my fridge at 20 Degrees.
OG 1038

I smacked the Wyeast package a few hours before pitching it into the wort. Ive been reading about that particular yeast on craftbrewer and it says that diacetyl production is noticeable and a thorough rest is necessary. I have never done a rest or used this yeast before and I am wondering how you know when you are at the right stage in fermentation and what temperature you raise it to. Also wondering what peoples experiences have been with this yeast. Any help would be very much appreciated.

Cheers, Jim

[warra48]

I did 3 batches in a row with this yeast, but I had mine in the fermenter for 2½ weeks on each occasion, but controlled the temperature to no more than 19ºC.
I'm drinking some now where I used this yeast, and I can't say I notice any particular diacetyl character.

I imagine if you ferment warmer, and bottle after say only a week, then you might notice it.
It's a yeast which seems to like to get on with the job early on in its life, but which will continue to work very slowly after the initial burst.

I'd say, just give it enough time to clean up after itself, and you'll be fine. No harm in leaving it in primary for up to 3 weeks.

One other thing, this yeast really floculates in the fermenter like no other I've ever seen.
Once you bottle, you will still have enough yeast in suspension, but you'll need to be patient to wait for it to carb up.

Of course, if you keg, you'll have no such concerns.

[drsmurto]

Like Warra, i leave my beers in primary for a minimum of 2 weeks.

I have used 1968 once and didn't notice any diacetyl and regularly used 1187 (ringwood) which is supposed to produce significant amounts of diacetyl as well.

In lager brewing you normally* raise the temp towards the end of primary fermentation. There is no reason you cant do this with an ale yeast. I tend to push my english ale yeast at the high end of the temp scale for the whole primary ferment rather than raising the temp.

Cheers
DrSmurto

* I don't do diacetyl rests with any beer. Pitch enough healthy yeast at fermentation temp and allow it enough for the yeast to mop up the by-products and its not necessary (in my unqualified opinion only)

[jab]

Thanks for the help guys. Im going to leave this one in the primary at 20 degrees for 2 weeks so that should take care of any diacetyl issues. This is the second liquid yeast Ive used so Im keen to see how it turns out.

Cheers, Jim

[Trough Lolly]

Hi Jim,
Wyeast 1968 is apparently not too dissimilar to SO-4, ie, they're allegedly from the same Fullers strain. I don't think diacetyl is a big issue and to be more exact, yes, some strains do have the propensity to emphasise the diacetyl in beer, but its not exactly the yeast itself that causes the diacetyl in the beer. To save me more typing, let me quote from a post I made on aussiehomebrewer back in 2006:

There are, however two problems that make the elimination of diacetyl quite challenging. The first problem is the presence of the precursor to diacetyl and the second problem is the characteristics of the yeast strain itself.

The generation of diacetyl in beer is not actually dependent on the yeast. The diacetyl precursor - alpha acetolactate - undergoes a spontaneous oxidative decarboxylation and converts into diacetyl (2,3-butanedione). Two major influences in this process are pH and temperature (there are, of course, other factors including oxygen levels and oxidative ions such as iron or copper that also convert the precursor to diacetyl).

Taking a step backwards, we need to understand how the alpha acetolactate got there in the first place and the prime culprit is the yeast itself - generating the alpha acetolactate as a result of synthesising valine and leucine amino acids from the wort during the "active" or attenuative phase. The fact is that if we could use a yeast strain that didn't generate any alpha acetolactate, or we got hard core and added alpha acetolactate decarboxylase that converts the alpha acetolactate to acetoin and bypasses the diacetyl stage, we wouldn't have any diacetyl. The yeast strains that we use do unfortunately secrete alpha acetolactate, but that rate of secretion does vary between strains.

So, the problem we have is active yeast that yes, is quite capable of scrubbing out the diacetyl present in the fermenting wort, but at the same time, is quite possibly still secreting the diacetyl precursor. And this is why I'm not all that convinced that giving the beer a diacetyl rest when the attenuative phase is not complete, is the best solution. Yes, it works, but it's possible that the diacetyl rest is better done in the window of opportunity between the end of primary fermentation and when the yeast is flocced out and dormant, ie there is still yeast in suspension, before lagering, that still have diacetyl reductases present to scrub the diacetyl out of the fermented wort...

This is demonstrated by brewers who experience "late bloom" diacetyl in their beer. They can't detect any diacetyl when fermentation has completed and they do a short diacetyl rest then rack to lagering or simply skip the rest and rack the diacetyl free beer straight to lagering, only to find to their dismay the presence of diacetyl some weeks later when they sample from the lagering vessel....Why is this so?!

A common answer is oxygen - unless you rack under CO2, you can inadvertantly add oxygen during racking into the lagering vessel and that oxygen converts the alpha acetolactate present in the pre-lagered beer, into diacetyl. And of course, since you lagered the beer, the yeast is inactive so it won't clean the diacetyl up...

Let me apologise for rabbiting on, but I'm not convinced that a diacetyl rest should be rushed into - I see your logic but it gets easily contradicted by the active yeast taking on the role of prime culprit in the precursor generation stakes. Perhaps the generation of the alpha acetolactate drops off substantially as we near the end of the attenuative phase - I don't have clear data on that, but I'm gonna stick to my standard procedure and do the diacetyl rest at the end of the primary fermentation and not beforehand....

The original thread is here...

Cheers,
TL